Hyaluronic acid is a naturally occurring mucopolysaccharide consisting of alternating D-glucuronic acid and N-acetyl D-glucosamine monomers. It is present in connective tissues and plays a vital role in many biological processes such as tissue hydration, proteoglycan organization in the extra-cellular matrix, and cell differentiation. Because of its important biological roles, hyaluronic acid has been widely exploited in medical practice for use in treating many different conditions. Several hyaluronic acid containing products are currently marketed for pharmaceutical or veterinary use, including a product for intra-ocular injection during eye surgery, synovitis agents for veterinary use, and coated gauzes for wound dressings.
Through the esterification of carboxyl groups of hyaluronic acid with various therapeutically inactive and active alcohols, it has been possible to synthesize biopolymers with medically desirable properties that are significantly different from those of hyaluronic acid itself. The biocompatibility of these altered molecules appears to be quite good. For example, a chemically modified form of hyaluronic acid "HYAFF-11" prevents fast enzymatic degradation in vivo and degrades slowly in concert with new tissue formation. The HYAFF-11 material is commercially available as skin repair products for wound and burn patients.
The following depicts the structure of hyaluronic acid. ##STR1##
The carboxyl group of hyaluronic acid can be replaced with various moieties, including molecules such as ethyl, propyl, pentyl, benzyl or larger molecules such as hydrocortisone or methyl prednisolone. Reaction conditions can be controlled so as to influence the degree of substitution on the hyaluronic acid molecule, thereby further influencing the properties of the final product.